1. Field of the Invention
The invention relates to a heating roller for fixation in a fixation device used in image formation devices such as copiers, printers, and facsimile devices, and relates especially to a heating roller for fixation in which a resistance heating member is formed in a sheet shape and is anchored inside the roller.
2. Description of the Related Art
Conventionally, with an image formation device using the fixation type of electronic photographing technology, for example, a laser printer, a heat roller in which a halogen lamp is used as the heat source is widely adopted as the fixation device. A fixation device which uses this type of heat roller (FIG. 6) is provided with a heating roller for fixation 104 with a built-in halogen lamp 102 as the heat source. A pressure roller 106 opposes the heating roller for fixation 104. The heating roller for fixation 104 absorbs the radiation heat generated by the halogen lamp 102, causing the heat of the heating roller for fixation 104 to rise to the fixation optimum temperature. The toner image 108 is fixed on a recording medium 110 by the heating of the recording medium 110, which carries the toner image 108, as the recording medium 110 is transported between the heating roller for fixation 104 and the pressure roller 106 by their rotation (arrows).
A temperature sensor 112 is installed so as to contact the heating roller for fixation 104. The electric power applied to the halogen lamp 102 is feedback-controlled based upon the detected temperature of the heating roller for fixation 104. Moreover, a peeling layer 114, composed of fluoride resin or the like, is formed on the surface of the heating roller for fixation 104 to prevent the toner and the recording medium 110 from becoming attached to and wrapping around the heating roller for fixation 104.
With this type of fixation system, the halogen lamp is installed in the center of the hollow heating roller for fixation without adhering to the surface of the roller. Hence, heat efficiency is poor, creating the problem that the time interval between the start of supplying electric current to the halogen lamp 102 and the point at which the heating roller for fixation 104 reaches the predetermined temperature suited for fixation of the toner is too long. As a result, different types of heating rollers for fixation have been suggested to shorten this time interval.
For example, Japanese Unexamined Patent Publication Sho 62-279378 discloses a heating roller for fixation in which a resistance heat generating layer, to be used as a heat source, is provided on the inner surface of the heating roller for fixation. In such a fixation device, the heating roller for fixation, with the built-in resistance heat generating layer on its inner surface as the heat source, the pressure roller to press against the heating roller for fixation, and a pair of power supply members which make contact, from the inside, with both sides of the resistance heat generating layer, are provided. The resistance heat generating layer is heated by the electric current supplied by the power supply members, wherein the heating roller for fixation absorbs the heat, causing the temperature to rise to the fixation optimum temperature. At that time, the toner image is fixed on the recording medium by the heating of the recording medium carrying the toner image while the recording medium is transported between the heating roller for fixation and the pressure roller. An insulating layer is provided between the main body of the heating roller for fixation and the resistance heat generating body to insulate the two bodies. Moreover, the power supply members comprise a mechanism which operates symmetrically to the central location of the heating roller for fixation, enabling efficient heating which adjusts to the width of the recording medium. In addition, a peeling layer, composed of a fluoride resin or the like, is formed on the surface of the heating roller for fixation to prevent the toner and the recording medium 110 from attaching to and wrapping around the heat roller for fixation, in a similar fashion as in the previously described device.
However, in a fixation device based on the heat roller method using the above-stated resistance heat generating layer as a heat source, an insulation layer is first formed to insulate the resistance heat generating layer from the inner surface of the heat roller for fixation. Then the resistance heat generating layer is formed on the inner surface of the insulating layer thus formed. Thus, the manufacturing steps to form the resistance heat generating layer in addition to the insulating layer are increased, resulting in the problem that a large amount of time is required for production of the heating roller for fixation. Moreover, such work processes clearly become more complicated as the inner diameter of the roller within the roller body becomes smaller.
Moreover, because the amount of heat radiated from the ends, in the direction of the axis of the heating roller for fixation, is large, the temperature at both ends tends to be lower than the temperature of the central area. Thus, it is necessary to generate more heat at the ends of the heating roller for fixation to make the temperature distribution uniform throughout. In such cases, the formation of the resistance heat generating layer, to make the temperature distribution of the heating roller for fixation uniform, becomes complicated, resulting in the problem that the time required to form the above-stated resistance heat generating layer increases further.
In order to solve the above problems, a method is considered in which the insulation layer and the resistance heat generating layer are formed on the outer surface of the roller body, but because the paper and the toner slide on the outer surface of the heat generating layer, problems occur in which the resistance heat generating layer is cut or it wears out quite quickly.